Valine

Valine


Valine is an α-amino acid with the chemical
formula HO2CCH(NH2)CH(CH3)2. L-Valine is one of 20 proteinogenic amino
acids. Its codons are GUU, GUC, GUA, and GUG. This essential amino acid is classified as
nonpolar. Human dietary sources are any proteinaceous
foods such as meats, dairy products, soy products, beans and legumes. Along with leucine and isoleucine, valine
is a branched-chain amino acid. It is named after the plant valerian. In sickle-cell disease, valine substitutes
for the hydrophilic amino acid glutamic acid in hemoglobin. Because valine is hydrophobic, the hemoglobin
is prone to abnormal aggregation. Nomenclature
According to IUPAC, carbon atoms forming valine are numbered sequentially starting from 1
denoting the carboxyl carbon, whereas 4 and 4′ denote the two terminal methyl carbons. Biosynthesis
Valine is an essential amino acid, hence it must be ingested, usually as a component of
proteins. It is synthesized in plants via several steps
starting from pyruvic acid. The initial part of the pathway also leads
to leucine. The intermediate α-ketoisovalerate undergoes
reductive amination with glutamate. Enzymes involved in this biosynthesis include:
Acetolactate synthase Acetohydroxy acid isomeroreductase
Dihydroxyacid dehydratase Valine aminotransferase
Synthesis Racemic valine can be synthesized by bromination
of isovaleric acid followed by amination of the α-bromo derivative
HO2CCH2CH(CH3)2 + Br2 → HO2CCHBrCH(CH3)2 + HBr
HO2CCHBrCH(CH3)2 + 2 NH3 → HO2CCH(NH2)CH(CH3)2 + NH4Br
References See also
Valinol External links
Valine MS Spectrum Isoleucine and valine biosynthesis

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